The present invention relates to the production of flat shavings, especially from residues or scraps of wood. More particularly, the invention relates to a multi-stage process and apparatus for conversion of regularly or irregularly shaped pieces of wood into shavings of predetermined size and shape. Such shavings can be used for the manufacture of chipboard or particle board panels and may be obtained by further processing of residues or scrap from millwork, furniture or plywood manufacturing and similar operations.
It is already known to convert scrap wood (such as planks, slabs, rinds, splinters, fragments of logs, residue of plywood sheets or veneers) into chips by resorting to so-called drum- or disk-type comminuting machines. It is further known to reduce the size of such chips by resorting to knives (see German Auslegeschrift No. 2,332,121) or to rotary disks (as disclosed, for example, in German Offenlegungsschrift No. 1,942,531). The resulting shavings are ready to be utilized in the manufacture of particle board panels. The maximum length of shavings equals the maximum length of chips. It has been found that the quality and homogeneousness of shavings which are produced in accordance with the just outlined procedures (i.e., conversion of scrap wood into chips and conversion of chips into shavings) are not predicable to an extent which is necessary for the production of high-quality particle board panels. Thus, the homogeneousness of such shavings is invariably inferior to that of shavings which are produced by comminuting machines employing knife shafts. This is attributable to the fact that the orientation of grain is different from chip to chip. Consequently, comminution of chips results in an undesirably high percentage of short fragments because the chips do not tend to and infrequently assume such positions that their conversion into shavings takes place by subdivision in planes which are parallel to the grain. In other words, a high percentage of chips is severed in such a way that the cutting planes are normal to or make oblique angles with the longitudinal direction of the fibers. It was further found that chips of average length (normally between 30 and 40 millimeters) tend to break at right angles to the longitudinal direction of fibers, especially if the moisture content of wood is relatively low. This further contributes to the presence of undesirably high percentages of unsatisfactory fragments which are smaller than the optimum size of shavings in a particle board panel. Therefore, manufacturers of particle board panels or like products which consist of or contain a high percentage of wood shavings are reluctant to employ only shavings which are obtained from residues in spite of the obvious economical advantages of such procedure. In other words, and as a rule, particle board panels which are obtained on the market invariably contain a rather high percentage of shavings which are obtained from valuable wood, i.e., from wood which does not constitute remnants of logs, boards, beams and other wood products in millwork, manufacture of furniture, plywood and other woodworking operations.